This research program involves a number of investigators who perform studies on patients with certain neoplastic diseases, patients with chronic renal failure who received renal allografts and upon animal models (calves and sheep) who receive allografts. Patients with neoplastic diseases such as acute myelo-monocytic leukemia in remission undergo cannulation of the thoracic duct. Thoracic duct lymph is collected and the lymphocytes are harvested for a period of 48 hours. Following this procedure the patients are treated with large doses of cytotoxic agents followed by the reinfusion of their circulating lymphocytes. This technique is being employed to attempt to induce long remissions in this neoplastic disease. Thymosin dynamics are studied in patients undergoing the depletion of circulating lymphocytes by means of thoracic duct drainage. These investigations have been undertaken to understand the physiologic significance of thymosin and to explore the possibility of the therapeutic usefulness of this humoral factor. Patients with chronic renal failure are prepared for renal transplantation by means of 4-6 weeks of thoracic duct drainage. The collected lymph is centrifuged and the cell-free lymph is reinfused daily. After 4-6 weeks profound lymphocytopenia develops with circulating lymphocyte level ranging from 200-400 lymphocytes per cu. mm. Peripheral lymphoid tissues also demonstrate profound depletion of lymphocytes. However, these patients and the animal models maintain reasonably normal levels of immunoglobulins and maintain satisfactory defenses against common bacterial infections. Numerous investigations of the immunologic systems of these patients and the animal models are being conducted. For example, investigations have been initiated to characterize the lymphocytes contained in thoracic duct lymph as the depletion of lymphocytes progresses. Both functional and morphologic characterization of these cells are under investigation.